Hydraulic reservoir in particular a membrane reservoir

ABSTRACT

The invention relates to a hydraulic reservoir in particular a membrane reservoir, with a gas inlet body ( 12 ) which may be connected to parts of the reservoir housing and which comprises at least one mounting surface ( 28 ) for an elastically flexible separating element ( 16 ), which separates two chambers arranged within the reservoir housing from each other. The separating element ( 16 ) comprises a edge reinforcement ( 30 ) formed by material thickening to give a fixing edge for that part with the corresponding mounting surface ( 28 ) of the gas inlet body ( 12 ). Failures at the position of the fixing of the separation element to the hydraulic reservoir are avoided, despite high loading of the separating element under working conditions for the reservoir, whereby the edge reinforcement ( 30 ) is provided with a convex guide surface on the side thereof facing the gas inlet body ( 12 ) in contact with the corresponding mounting surface ( 28 ), which is at least partly concave in embodiment to match said unit.

The invention relates to a hydraulic accumulator, a bladder accumulatorin particular, having a gas inlet element which may be connected toparts of the accumulator housing and which has at least one mountingsurface for an elastically flexible separating element which separatesfrom each other two chambers positioned inside the accumulator housing,the separating element having an edge reinforcement in the form ofthickening of the material to form a fastening edge for the respectivecontact with the associated mounting surface of the gas inlet element.

Hydraulic accumulators of this type, which are preferred for use inhydraulic systems, perform a variety of functions, especially in theareas of energy storage, emergency actuation of assemblies, shockabsorption, pulsation damping, etc. The general principle of operationof hydraulic accumulators is that of storage of compression energy,while the mode of operation of such accumulators having separatingelements is based on the compressibility of a gas which is received intothe gas chamber of the accumulator and is used for variable liquidstorage inside the liquid chamber of the accumulator, the separatingelement separating the gas chamber from the liquid chamber and theliquid chamber being periodically connected to a hydraulic circuit sothat when the pressure increases the gas is compressed on the gas sideand when the pressure drops on the fluid side the compressed gas mayexpand and as a result the liquid stored is again forced into thehydraulic circuit.

Hydraulic accumulators with a separating element are in general dividedinto bladder accumulators, diaphragm accumulators, and pistonaccumulators, the present invention being employed by special preferencein bladder accumulators which are provided with an elastically flexibleseparating element, preferably one in the form of a separatingaccumulator bladder. The accumulator bladder, in the form of aseparating diaphragm, is charged periodically by the gas valvepositioned on the upper part of the accumulator, which forms a sort ofgas inlet element. The liquid valve mounted on the lower end of thehydraulic accumulator primarily prevents drawing of the accumulatorbladder out by suction as the fluid flows out. The separating element inthe form of the accumulator bladder is subjected to very high pressurechange stresses and accordingly is highly stressed. The separatingelement is essentially kept open in the direction of the fluid side ofthe hydraulic accumulator and acts directly on the fluid side of theaccumulator. At the opposite end, on the other hand, the separatingelement is rigidly connected to the gas inlet element, a reinforced edgein the form of thickening of the material being retained by clampingbetween the gas inlet element and the associated interior wall elementsof the accumulator housing. In order to achieve good retention, in thedisclosed solutions additional provision is made such that diaphragmparts of the accumulator bladder extend below the bottom of the gasinlet element, the entire area of which, except for an inlet and anoutlet opening, is attached to the bottom of this gas inlet element. Thefastening force may be further increased by gluing or vulcanizing thegas inlet element in the form of the gas valve in the opening of theseparating element, preferably in the form of the accumulator bladder.

Despite the well tested procedure of fastening the separating elementinside the housing of the hydraulic accumulator, failure of the entirehydraulic accumulator may occur as a result of processes of separationof the separating element by tearing which may occur precisely in theareas in which it is fastened. Failure of the fastening option is alsopossible in the event of vulcanizing of the gas inlet element into theunobstructed opening in the separating element, in particular as aresult of the high alternating stresses in this separating element. Ithas also been found that unintentionally high stresses at the site ofconnection involving the risk of failure may occur as a result of thetype of fastening described in the foregoing.

On the basis of this state of the art, the object of the invention is toeffect further improvement in the known hydraulic accumulators, bladderaccumulators in particular, so that, despite the high stresses to whichthe separating element is subjected during operation of the accumulator,instances of failure are prevented at the site of the fastening of theseparating element to the hydraulic accumulator. The object as thusformulated is attained by means of a hydraulic accumulator having thecharacteristics specified in claim 1 in its entirety.

In that, as specified in the characterizing part of claim 1, the edgereinforcement is provided with a convex guide surface on its side facingthe gas inlet element, which side is in contact with an associatedmounting surface which is configured to be at least in part concave forthe respective mounting, both a reliable possibility of fastening theseparating element on the hydraulic accumulator housing is achieved andthe fastening in question is effected by a gentle method, which does notharm the edge reinforcement and so tends to lengthen the service life ofthe connection. As a result of the convexity of the guide surface of theseparating element, an annular surface in contact with the associatedmounting surface of the gas inlet element, a sort of articulation isachieved and the separating element may correspondingly develop aroundthe articulation and execute restricted movements, without introductionof harmful forces into the fastening point.

It is especially advantageous for formation of the articulation inquestion for the convex guide surface of the separating element toeffect transition in the direction of its bottom partly into a concavedevelopment surface.

In one preferred embodiment of the hydraulic accumulator claimed for theinvention the mounting surface of the gas inlet element communicateswith a discharge slope, the angle of inclination of which encloses anacute angle with an imaginary plane transverse to the longitudinal axisof the hydraulic accumulator. On the basis of the respectiveconfiguration there is created for movement of the separating element asort of free running surface which makes it possible for the separatingdiaphragm to be oriented in the direction of the discharge slope inquestion even in the event of very high expansion stresses, so thatgentle movement of the separating element is made possible withoutintroducing forces harmful to the fastening point.

Provision preferably is made such that the discharge slope of the gasinlet element undergoes transition in the direction of its bottomcomponent into a camber designed to be convex.

If in another preferred configuration of an embodiment of the hydraulicaccumulator claimed for the invention the discharge slope is providedwith a support for the edge reinforcement with its convex guide surface,such provision makes certain that the fastening point illustrated cannotbe unintentionally loosened when the separating element is subjected toextreme stresses. The support in question rather ensures that the edgereinforcement will remain in its fixed position at the fastening point.

In another preferred embodiment of the hydraulic accumulator claimed forthe invention, the edge reinforcement has additional reinforcement onthe side facing the accumulator housing. After the hydraulic accumulatorhas been assembled, this additional reinforcement is tightly fittedbetween at least one of the mounting surfaces of the gas inlet elementand the associated wall component of the accumulator housing. Despitethe increase in the force applied in the area of connection in question,care is nevertheless taken by way of the additional reinforcement thatstress on the connection as a whole is relieved and that the compressiveand tensile forces introduced into the separating element cannot have aharmful effect on the area of the connection point, so that incidents offailure are accordingly significantly reduced. It is a surprise to theexpert in the field of hydraulic accumulators to learn that, despiteincrease in the forces of application in the area of fastening, reliefof the forces introduced rather occurs in this area, and, in addition tothe increased reliability of retention, processes of tearing of theelastic separating element are largely prevented in this area. Acontribution to this result is made by the circumstance that the forcesof application introduced in the area of transition between parts of theaccumulator housing and the additional reinforcement of the separatingelement are jointly absorbed by the concave associated mounting surfaceof the gas inlet element so as to prevent damage to the separatingelement.

In another preferred embodiment of the hydraulic accumulator claimed forthe invention, the additional reinforcement is in the form of areinforcing ring which is offset to the back from the open end of theseparating element or effects transition to a plane common with that ofthis separating element. Provision preferably is made such that thereinforcing ring is in the form of a ridge which is an integral part ofthe separating element and is semicircular, rectangular, or triangularin cross-section. Selection of the respective geometric form of theridge makes it possible to achieve gentle linear or planiform contactbetween the separating element and the associated parts of theaccumulator housing, so that the fastening may be adapted with precisionand certainty to the stresses occurring in the individual instance as afunction of the application problem involved which is to be solved.

Provision preferably is made such that the open end of the respectivefastening ridge is provided with a convex camber; this affords theadvantage that transitional areas with sharp edges are avoided, oneswith might favor harmful introduction of forces into the area of thefastening edge.

In another preferred embodiment of the hydraulic accumulator claimed forthe invention, the additional reinforcement of the separating element isreplaced by provision of a recess on the interior side of the associatedparts of the accumulator housing, so that adequate space is provided forseating of the edge reinforcement of the separating element. Theadditional reinforcement may rest on surfaces of the recess and thusensure retention of the fastening edge in its position, as well asprevention of impermissibly high compressive forces on the fasteningedge of the separating element. The possibility also exists of supportof the accumulator housing parts by separating element segmentspositioned farther outward in the radial direction; this as well hasbeen found to be favorable for introduction of forces to the site oftransition between the separating element and the fastening edge.

In one especially preferred embodiment of the hydraulic accumulatorclaimed for the invention, the course of curvature of the accumulatorhousing in the interior of the latter in the area of contact with theseparating element is steeper than that of the separating element in theunactuated initial state, the respective curvature being designed to besteeper than that of the separating element when fastened. The differentcourses of curvature of wall components of the accumulator housing andof the separating element also make it possible to achieve full-areacontact in the area of contact when the accumulator has been actuated,and as a result of the frictional forces which occur, these forcesseeking to retain the separating diaphragm on the inside of theaccumulator housing on the fastening edge in the area of transition, therespective fastening components are relieved of stresses, this resultingin significant additional increase in the service life of the hydraulicaccumulator.

The hydraulic accumulator claimed for the invention will now bedescribed in greater detail below with the aid of three exemplaryembodiments illustrated in the drawings, in which, in the form ofdiagrams not drawn to scale,

FIG. 1 shows a bladder accumulator (hydraulic accumulator) such as is ofthe state of the art, partly as a front view and partly in longitudinalsection;

FIGS. 2 to 4 show, in cross-section, three different options forconnecting the respective separating element to the associated gas inletelement;

FIGS. 5, 6, and 7 shown three different options for fastening associatedparts of the accumulator as shown in FIG. 2 at the fastening point.

The state-of-the art hydraulic accumulator, in the form of a bladderaccumulator, is published in the book issued by Mannesmann-Rexroth GmbHADer Hydraulik-Trainer@ [The Hydraulics Trainer], Volume 3, firstedition, page 100. This known hydraulic accumulator has an accumulatorhousing 10, on the upper side of which there is mounted a gas inletelement 12 in the form of a conventional gas valve provided for thispurpose. The accumulator housing 10 is provided on its lower side with apoppet valve assembly designated as a whole as 14. A separating element16 in the form of an accumulator bladder of elastomer material (rubberdiaphragm material) is mounted inside the accumulator housing 10. Theseparating element 16 in question divides the hydraulic accumulator intoa gas chamber 18 and a fluid chamber 20. When fluid flows in by way ofthe poppet valve assembly 14, the working gas, mostly in the form ofnitrogen gas, enclosed in the separating element 16 so as to befluid-tight is compressed and the energy thus stored on the gas side maylater be delivered if necessary to the fluid side of the accumulator andthus in turn to the fluid chamber 20, the associated separating element16 then being expanded by the action of the working gas. If theaccumulator is fully emptied of fluid on its fluid side, the separatingelement 16 can actuate the poppet valve assembly 14 by way of its lowerside and the poppet valve is closed in the conventional manner againstthe force of a reset spring. The respective structure of a hydraulic orbladder accumulator is a conventional one, and accordingly all thedetails of such accumulators will not be discussed at this point.

The gas inlet element 12 in the form of the gas valve is provided with acover 22 in the form of a cap and, as is shown in FIG. 1, the gas inletelement 12 is designed to engage the accumulator housing 10; the gasinlet element 12 may for this purpose be screwed into the free openingof the accumulator housing 10 by way of conventional external threading24 (see FIG. 2 and following). In the known solution the separatingelement 16 is provided with the associated mounting surface 28 of thegas inlet element 12 to form a fastening edge 26 for the respectiveassembly, the fastening edge 26 having an edge reinforcement 30 in theform of thickening of the material in this area. In the case of theknown solution shown in FIG. 1, an additional fastening option is alsoprovided in that, on the lower side (bottom part) of the gas inletelement 12 the separating element 16 extends below the respective end asfar as an inlet opening 32 and in doing so forms a flat support surface34. Despite this additional support surface 34, in the event of highcompression and application of tensile stress to the separating element16, it is possible for this element to be torn off in the area oftransition to the fastening edge 26 or for it to become porous at thesesites, something which in both instances may result in failure of theentire hydraulic accumulator. If one is reluctant to wait for therespective event of failure, the separating element 16 in the form ofthe accumulator bladder is to be replaced at prescribed maintenanceintervals by decommissioning the hydraulic accumulator.

In order to prevent the failure in question, provision is made by thesolution provided by the invention as illustrated in FIG. 2 such thatthe edge reinforcement 30 is provided on its side facing the gas inletelement 12 with a convex guide surface 36 which is in contact with theassociated mounting surface 28, which is configured to be at least inpart concave. The concave mounting surface 28 of the gas inlet element12 communicates with an outlet slope 38, the angle of inclination 40 ofwhich encloses an acute angle, preferably of approximately 25°, with animaginary plane 42 extending transversely to the longitudinal axis ofthe hydraulic accumulator.

As is shown in FIG. 4, in order to increase the retention forces for thefastening edge 26, in a modified embodiment the respective outlet slope38 may be provided with a support 46 which secures the edgereinforcement 30 with its convex guide surface 36.

In the area of transition between the separating diaphragm 16 asaccumulator bladder and the edge reinforcement 30, as is shown in FIG. 2and following, the convex guide surface 36 effects transition to aconcave development surface 48. The respective development surface 48makes it possible, even in the event of strong compressive movements ofthe separating membrane 16, for this membrane to develop on the convexoutlet slope 38 of the gas inlet element 12 in order thus to protect theclamping point on the edge reinforcement 30 from harmful introduction offorces. Consequently, the transition from convex guide surface 36 toconcave mounting surface 28 of the gas inlet element 12 forms a sort ofarticulation or hinge point so that the separating diaphragm 16 maydevelop gently between gas inlet element 12 and inside of theaccumulator housing 10. Even if the gas inlet element 12 is configuredwith a support 46, as is shown in FIG. 4, the separating membrane 16 maydevelop around this support with precision without harmful kinks andintroduction of impermissibly high tension into the separating element16.

In one especially preferred embodiment, provision is made such that theedge reinforcement 30 has on its side facing the accumulator housing 10an additional reinforcement 50 which, when the accumulator has beenassembled, is compressed between at least one of the mounting surfaces28 of the gas inlet element 12 and the interior wall elements of theaccumulator housing 10. In the embodiment shown in FIGS. 2 and 4, theadditional reinforcement 50 consists of a reinforcing ring or bead whichis more or less triangular in cross-section, the open end of theadditional reinforcement 50 being provided with a camber toward theexterior, in order thus to obtain two-dimensional sealing contact withassociated internal wall elements of the accumulator housing at thepoint of fastening. Consequently, in these embodiments the additionalreinforcement 50 communicates in a common plane with the parts of theguide surface of the fastening edge 26 which are oriented in parallelwith the longitudinal axis 44 of the accumulator housing 10. In the formof embodiment shown in FIG. 3, the reinforcing ring is configured to besemicircular in cross-section and is mounted so as to be offset to theback from the frontal guide surface opposite the gas inlet element 12.Because of the outline on the external circumference side of theadditional reinforcement 50, two-dimensional contact with the associatedinterior wall elements of the accumulator housing is ensured, so thatreliable sealing is ensured in these areas as well.

FIG. 5 and following illustrate installation of the configuration shownin FIG. 2 inside the accumulator housing 10 of the hydraulic accumulatoras a whole shown in FIG. 1, after this housing has been mounted. For thesake of greater clarity of illustration, however, the accumulatorhousing part 10 in FIGS. 5, 6, and 7, is not shown in its position afterhaving been screwed tightly onto the gas inlet element 12, so that therelationships at the point of clamping may be more clearly illustrated.

In the embodiment shown in FIG. 5, the interior of the accumulatorhousing 10 has in the area of application with the edge reinforcement 30a recess 52 which is formed by reducing the wall cross-section of theaccumulator housing 10 in the direction of the open end of the openingin this housing. After installation the edge reinforcement 30 with itsbead-like widened area accordingly rests also on the interior wall ofthe recess 52 in the radial direction, so that the fastening edge 26 issecurely fastened to the gas inlet element 12. In the embodimentillustrated in FIGS. 6 and 7 the recess 52 shown in FIG. 5 is in theform of corresponding recess slopes 54, but these slopes exertessentially the same effect and ensure all-over contact over large areasof the accumulator housing 10 in the area of the fastening point, alongwith correspondingly high frictional forces between separating element16 and accumulator housing 10, something which contributes to moresecure fastening.

As shown also in FIG. 5 and following, the course of curvature of theaccumulator housing 10 in the area of contact with the edgereinforcement 30 is steeper than the separating element 16 in theinitial state before actuation, the curvature in question being designedto be steeper than that of the separating element 16 after it has beenfastened. In order to illustrate the radii of curvature, in the drawingsin FIGS. 5, 6, and 7, the separating element 16 below its fastening edge26 is shown symbolically to extend in part inside the accumulatorhousing 10, while the actual relationships are such that the upper sideof the elastomer separating element 16 is guided in this area over apredetermined frictional section along the inside of the accumulatorhousing 10. The separating element 16 is relieved of forces of frictionby way of the frictional stretch as configured on its fastening edge 26,with the result that peaks of force introduction are reliably absorbedin this way before they reach the point of clamping and can exert theireffect. This last-named circumstance significantly lengthens the servicelife of the clamping feature of the separating element 16 inside avariety of hydraulic accumulator housings.

In order to retain the gas inlet element 12 in its installed position onthe open end of the separating element 16, provision preferably is madesuch that the diameter chosen for the free end of the separating element16, bounded by the fastening edge 26, is significantly smaller than theexternal circumference of the gas inlet element 12 below the externalthreading 24. Consequently, when the gas inlet element 12 has beenintroduced, the free, open end of the separating element 16 is expandedand, as a result of the elastic rubber tension, the gas inlet element 12is immobilized in its installed position in the separating element 16.As an alternative or in addition, provision may also be made such thatpermanent mounting of the separating element 16 on the gas inlet element12 is achieved by way of a bonding agent (primer) or an adhesivecompound.

If the separating element 16 is pretensioned before being mounted on thegas inlet element 12, a reliable barrier is formed the effect of whichmay be increased by way of the additional reinforcement 50, so that, forexample, if aggressive fluid media are used in place of the conventionalhydraulic medium, the gas side is securely separated from the fluid sideand in this way damage to the gas inlet element 12 by the aggressivemedium may also be prevented.

1. A hydraulic accumulator, a bladder accumulator in particular, havinga gas inlet element (12) which may be connected to parts of theaccumulator housing (10) and having at least one mounting surface (28)for an elastically flexible separating element (16) which separates fromeach other two chambers (18, 20) positioned inside the accumulatorhousing (10), the separating element (16) having an edge reinforcement(30) in the form of thickening of the material forming a fastening edge(26) for the respective contact with the associated mounting surface(28) of the gas inlet element (12), characterized in that the edgereinforcement (30) is provided on its side facing the gas inlet element(12) with a convex guide surface (36) which is in contact with theassociated mounting surface (28) which is configured to be at least inpart concave for the respective contact.
 2. The hydraulic accumulator asclaimed in claim 1, wherein the mounting surface (28), configured to beconcave, of the gas inlet element (12) communicates with an outlet slope(38) the angle of inclination (40) of which encloses an acute angle withan imaginary plane (42) extending transversely to the longitudinal axis(44) of the hydraulic accumulator.
 3. The hydraulic accumulator asclaimed in claim 2, wherein the outlet slope (38) is provided with asupport (46) for the edge reinforcement (30) with its convex guidesurface (36).
 4. The hydraulic accumulator as claimed in claim 1,wherein the edge reinforcement (30) has on its side facing theaccumulator housing (10) an additional reinforcement (50) which, whenthe accumulator has been assembled, is compressed between at least oneof the mounting surfaces (28) of the gas inlet element (12) and theassociated wall elements of the accumulator housing (10).
 5. Thehydraulic accumulator as claimed in claim 4, wherein the additionalreinforcement (50) is in the form of a reinforcing ring which is offsetto the back from the open end of the separating element (16) or whicheffects transition at this open end to a common plane with theseparating element (16).
 6. The hydraulic accumulator as claimed inclaim 5, wherein the reinforcing ring is in the form of a bead which, asan integral component of the separating element (16) is semicircular,rectangular, or triangular in cross-section.
 7. The hydraulicaccumulator as claimed in claim 6, wherein the free end of the bead isprovided with a convex camber.
 8. The hydraulic accumulator as claimedin claim 4, wherein, at the site of the additional reinforcement (50) ofthe separating element (16), the associated parts of the accumulatorhousing (10) are provided on their inside with a recess (52).
 9. Thehydraulic accumulator as claimed in claim 1, wherein the course ofcurvature of the accumulator housing (10) in the interior of the latterin the area of contact with the separating element (16) is steeper thanthat of the separating element (16) in the unactuated initial state, andwherein the respective curvature is designed to be steeper than that ofthe separating element (16) when fastened.